Electrophotographic copying machine

ABSTRACT

An improvement of an electrophotographic copying machine is provided in which a plurality of grounded grid electrodes are interposed between image forming means and surface of a photosensitive member of the type comprising an electrically conducting support, a photoconductive layer and an insulating layer, wherein the image forming means includes a device for focusing a light image and simultaneously discharging the charged surface of the insulating layer. The perfect discharge of the surface of the photosensitive member can be attained with this apparatus an image having a high contrast, excellent tone reproducibility and uniform sensitivity may be reproduced without being adversely affected by the environmental conditions.

United States Patent [191 Takahashi et al.

[ Mar. 19, 1974 ELECTROPHOTOGRAPHIC COPYING MACHINE [73] Assignee: CanonKabushiki Kaisha, Tokyo.

Japan [22] Filed: May 15, 1972 [21] Appl. No.: 253,235

[30] Foreign Application Priority Data 3.536.483 10/1970 Watonabe et al355/3 X 3.558.307 l/l97l Carlson 355/3 X 3.603.790 9/1971 Cleare 355/17Primary ExaminerSamuel S. Matthews Assisranl Examiner-15. M. BeroAttorney, Agent, or Firm-Fitzpatrick. Celia. Harper & Scinto [5 7]ABSTRACT An improvement of an electrophotographic copying machine isprovided in which a plurality of grounded grid electrodes are interposedbetween image forming means and surface of a photosensitive member ofthe type comprising an electrically conducting support, aphotoconductive layer and an insulating layer. wherein the image formingmeans includes a device for focusing a light image and simultaneouslydischarging the charged surface of the insulating layer. The perfectdischarge of the surface of the photosensitive member can be attainedwith this apparatus an image having a high contrast, excellent tonereproducibility and uniform sensitivity may be reproduced without beingadversely affected by the environmental conditions.

7 Claims, 11 Drawing Figures PAIENIEDm 19 :914

SHEET 1 0F 4 PRIOR ART PAIENIEBHAR 19 1914 3797 927 LIJ LU NO GRID EIOO- 5 w 20- 2p 4p 6 89% HUMIDITY WITH GRID IOO- PAIENIEDIIIIII I 9 I974BRET/L927 MU U 0? 4 NO GRID WITH GRID +36OV +300 (DARK) I O L I FIRSTSTEP SECOND 5% THIRD STEP (PRIMARY) IMAGE EXPOSURE (BLANKET CHARGESIMULTANEOU-SLY EXPOSURE WITH DISCHARGE ELECTROPHOTOGRAPHIC COPYINGMACHINE BACKGROUND OF THE INVENTION Field of the Invention discloses anelectrophotographic process in which a 1 photosensitive member comprisesthree layers consisting of an insulating layer, a photoconductive layerand an electrically conductive layer; or an insulating layer,

a photoconductive layer and an insulating layer; or four layersconsisting of an insulating layer, a photoconductive layer, aninsulating layer and a conductive layer. In the first step, the surfaceof the insulating layer of the photosensitive member is imparted with acharge of positive polarity when the photoconductive layer is of N typematerial or with a charge of negative polarity when the photoconductivelayer is of P type material so that a charge with the polarity oppositeto that of the charge imparted upon the surface of the insulating layeris bound in the vicinity of the interface between the photoconductinglayer and the insulating layer. In the second'step, simultaneously withthe projection of the light image of an original upon the surface of thecharged surface of the insulating layer, the a-c corona discharge or d-ccorona discharge with the polarity opposite to that of the chargeimparted in the first step is imparted to the surface of the insulatinglayer so that the charge pattern on the surface of the insulating layervaries depending upon the black and white or bright and dark pattern ofthe copy. In the third step, the photosensitive member is uniformlyilluminated by or exposed to the light blanket exposure so that thecharge in the vicinity of the interface between the insulating layer andthe photoconductive layer in the areas corresponding to the black ordark areas of the copy is released. Therefore, the electrostatic latentimage whose contrast is so high that it may be detected as a variationin surface potential may be formed upon the surface ofthe photosensitivemember. The electrostatic latent image thus formed is then developedinto a visible toner image with charged pigment particles, and the tonerimage is transferred onto a recording medium, which is generally paper,under the effect of the internal or external electric field. The tonerimage transferred onto the recording paper is fused and fixed to thepaper by heating with an infrared lamp. After the developed toner imagehas been transferred onto the recording paper, the surface of thephotosensitive member is cleaned to remove the remaining developingagent for reuse. In the process described above, the charge impartedonto the surface of the photosensitive member will not be dischargedonly by the exposure to the light or by the corona discharge so that thephotosensitive member must be discharged simultaneously by the lightexposure and the corona discharge imparted to the surface of thephotosensitive member.

In the electrophotographic process described above, it is very importantthat the surface potentials at the bright and dark areas have the samemagnitude when the light image is projected simultaneously with thedischarge of the surface of the photosensitive layer in the second step.The potential difference between the unilluminated or dark and theilluminated or bright areas adversely affects the contrast of theelectrostatic latent image. Therefore, it is preferred that thepotential difference is minimized so that a high contrast may beobtained. However, the prior art corona discharging device which hasbeen used in the second step of projecting the light image andsimultaneously imparting the charge with the opposite polarity, ordischarging the surface of the photosensitive member, is notsatisfactory for attaining the above described condition.

DESCRIPTION OF THE PRIOR ART In order to facilitate an understanding ofthe problems encountered in the prior art electrophotographic copyingmachines and of the advantage of the present invention, the prior artdevice for projecting a light image and simultaneously imparting acharge with a polarity opposite to that of the chargeimparted by thefirst step or the a-c corona discharge will be briefly described withreference to FIG. 1 prior to the description of the preferredembodiments of the present invention.

A corona discharge wire of tungsten or the like is extended between apair of spaced apart auxiliary electrodes 2 and 2 which define anoptical aperture at the upper ends and an opening for corona dischargeat the lower ends and which are generally grounded. A photosensitivemember 3 having an insulating layer, the surface of which must becharged or discharged, is disposed in opposed relation to the openingfor discharge of the device, and the high a-c voltage or the high d-cvoltage with its polarity opposite to that of the charge on the surfaceof the insulating layer is applied to the corona wire. The uniformdischarge of the surface of the photosensitive member 3 is effected whenthe latter is moved past the corona discharge electrode 1 and theauxiliary electrodes 2 and 2. The lower opening serves not only forimparting the charge to the surface of the photosensitive member 3 butalso for defining an optical slit through which the light image isprojected onto the surface of the photosensitive member. The prior artdevice has the advantages that it is simple in construction and that itmay discharge the surface of the photosensitive member without makingcontact with it, but it has the defect that when a d-c voltage isapplied, the discharge of the surface of the photosensitive memberbecomes very difficult, and the surface of the photosensitive member ischarged with the opposite polarity when the discharge speed is high.When an a-c voltage is applied, the surface of the photosensitive membermay be discharged to zero volt but the variations in the surfacepotential after the discharge, the discharge speed, the discharge speedvariation rate, and the discharge width are adversely affected by theenvironmental temperature and humidity and the variation in supplyvoltage. In the electrophotographic process of the type described above,in addition to the problem of the surface potential after the discharge,the above defects adversely affect the characteristics such as contrast,tone reproducibility, and uniform sensitivity, etc. of the electrostaticimage. Therefore, the image formation factors tend to change so that theadjustment of the electrophotographic copying machine becomes extremelydifficult.

SUMMARY OF THE INVENTION One of the objects of the present invention istherefore to provide an improved electrophotographic copying machinecapable of reproducing the image with the high contrast, the better tonereproducibility and the uniform sensitivity.

Another object of the present invention is to provide an improvedelectrophotographic copying machine in which the discharge or chargingin the second step of the electrophotographic process described abovefor projecting the light image and simultaneously charging ordischarging the surface of the photosensitive member can be accomplishedin an ideal manner so that a better image may be reproduced.

Another object of the present invention is to provide an improvedelectrophotographic copying machine in which a plurality of groundedgrid electrodes are disposed in the proximity of the charging ordischarging opening of the device used in the above-described secondstep of the electrophotographic process so that a better image may bereproduced.

Another object of the present invention is to provide an improvedelectrophotographic copying machine in which the arrangement of andespecially the spacing between the grid electrodes disposed in theproximity of the charging or discharging opening of the device used inthe second step are so adjusted that the better image may be reproduced.

Briefly stated, according to the present invention, a plurality ofgrounded grid electrodes are disposed in the proximity of the chargingor discharging opening of the device used in the abovedescribed secondstep, and the spacing between the adjacent grid electrodes is adjustedso that the rate of variation of the discharge speed, the dischargespeed, the discharged potential, and the relation between the dischargewidth and the exposure width may be controlled, thereby eliminating thedefects encountered in the prior art electrophotographic machinesdescribed above.

According to one aspect of the present invention, the surface of aphotosensitive member, consisting of a conductive support or base, aphotoconductive layer and an insulating layer which constitutes thesurface of the photosensitive member, is imparted with a positive ornegative corona charge depending upon whether the photoconductive layeris of N or P type material, and in the second step when the light imageis projected upon the surface of the photosensitive member, the surfacethereof is imparted with a charge with the polarity opposite to that ofthe charge imparted in the first step by the d-c corona discharge orimparted with a a-c corona discharge. In a device used in the secondstep, a plurality of grid electrodes are interposed between thedischarge means of the device and the surface of the photosensitivemember. In the third step, the whole surface of the photosensitivemember is illuminated or exposed to the blanket light. When the as ord-c corona discharge is made in order to remove the charge held on thesurface of the insulating layer of the photosensitive member, thesurface potential of the insulating layer approaches the groundedpotential of the grid electrodes so that the discharge may be muchenhanced. When the grid electrodes are not provided, the bright areashave surface potentials other than zero volt because the bright areashave electrostatic capacitances higher than those at the dark areas sothat the developing agent is apt to adhere to the bright areas, thuscausing fogs.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments thereof taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1a is a sectional view of a priorart device for projecting a light image and simultaneously dischargingthe surface of a photosensitive member;

FIG. 1b is a perspective view thereof;

FIG. 2 is a schematic side view of an electrophoto graphic copyingmachine in accordance with the present invention;

FIGS. 3a and 3a are sectional views of a device for projecting a lightimage and simultaneously discharging the surface of the photosensitivemember;

FIG. 3b is a perspective view thereof;

FIGS. 4a and 4a are sectional views of a device for projecting a lightimage upon and simultaneously discharging the surface of thephotosensitive member by the a-c corona discharge;

FIG. 4b is a perspective view thereof;

FIG. 5 is a graph illustrating the surface potential characteristiccurves of the prior art electrophotographic copying machine and thephotocopying machine in accordance with the present inventionincorporating the grounded grid electrodes; and

FIG. 6 is a graph illustrating the effect of humidity variation on thesurface potentials of the surface of the photosensitive member after thestep of projecting the light image upon and simultaneously dischargingthe surface of the photosensitive member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 2, aphotosensitive drum 4 which rotates in the direction indicated by thearrow has a photosensitive layer formed around the outer peripherythereof and consisting of an insulating layer 5, a photoconductive layer6 and an electrically insulating layer 7. Around the photosensitive drum4 are disposed a first charger 8 for imparting the charge with a desiredpolarity upon the surface of the photosensitive drum 4, and a device 9which imparts a charge with a polarity opposite to that of the chargeimparted by the first charger 8 or impart the corona charge imparted bythe first charger 8, or imparts an a-c corona when a light image of acopy is projected thereupon to form an electrostatic latent image. (Thedevice 9 will be referred to as asimultaneous-image-projection-and-charging device hereinafter forbrevity.) A grounded electrode grid is disposed in the lower opening ofthe device 9 in opposed relation to the drum 4. Next to thesimultaneous-image-projection-and-charging device 10 is disposed adevice for illuminating the whole surface of the photosensitive drum 4so that the contrast of the electrostatic image may be improved. Next tothe device 10 there is disposed a developing device 1 1 which is shownas comprising a dry process developing device having a magnetic or furbrush, but any wet process developing device of the type in which thephotosensitive drum is partially submerged into a developing liquidsolution or a developing liquid solution may be sprayed over thephotosensitive layer, may be employed. Next to the developing device 11is disposed a developed or toner image transfer device or roller 12 towhich is applied a bias voltage with the polarity opposite to that ofthe developing agent or toner so that a high efficiency is expected intransferring the toner image onto a recording medium P which isgenerally a sheet of paper. The recording paper P which is transportedby a feed roller 13 and a guide 14 is pressed against the toner imageupon the drum 4 by the transfer roller 12 so that the toner image may betransferred upon the recording paper P. In addition to the paper, theplastic sheets, the printing masters and the like may be used as therecording media. Next to the image transfer roller 12 is disposed therecording medium separating device which separates the recording paper Pfrom the'drum 4 so as to be fed through guide plates 15 into aheating-fixing device 16 where the toner is fused and fixed to therecording paper P. The copy is then discharged out of the photocopyingmachine.

The toner still remaining upon the surface of the photosensitive drum 4after the image transfer may be cleaned by a cleaning device 17 which isshown as comprising a fur brush in the instant embodiment, but may be ofany suitable type such as a rubber doctor blade.

FIGS. 3a and 3a show sectional views FIG. 3b shows and a partly explodedperspective view of the simultaneous-image-projection-and-chargingdevice which is denoted by 9 in FIG. 1. As illustrated the the gridwires 22 may be equally spaced as shown in FIG. 3a, or their spacing maybe varied as shown in FIG. 3a, wherein the distance between the wires isdecreased in the direction of movement of the layer 24, thusgradualizing the equalization of the surface charges. Corona dischargewires 19 are supported by supporting members 19, and a pair ofvertically spaced apart auxiliary electrodes 20 and 20' are disposedabove and below the corona discharge wires and form an opening fordischarge and an optical aperture through which the light image isprojected upon the drum. The optical aperture is closed with atransparent electrode 21, and grounded grid electrodes 22 are disposedbetween the surface of the drum 4 and the discharge opening and aresupported by supporting members 23.

The spacing between the grid electrodes 22 and the surface of thephotosensitive layer 24 is preferably one to three milimeters; thespacing between the grid electrodes 22 and the corona discharge wires18, 8 15 milimeters; and the spacing between the adjacent gridelectrodes 22, two milimeters. The grid electrodes 22 may be disposed inequidistantly spaced apart relation or in such a manner that thespacings between the adjacent grid electrodes may be gradually reducedas shown in FIG. 3b in order to improve the discharge effect because thedischarge speed is faster as the spacing between the adjacent gridelectrodes 22 is wider whereas the surface potential of thephotosensitive layer 24 approaches toward zero as the spacing becomesnarrower. In the process in which an electrostatic latent image isformed only when a light image is projected simultaneously when thedischarge is effected, the efficiency in light image projection may beenhanced when the discharge speed is faster so that the sensitivity maybe improved. Furthermore, the discharge time may be reduced so that thedark decay of the photosensitive layer may be decreased whereby thecontrast of the image may be enhanced. Experiments conducted by theinventors show that a contrast of 460 volts was attained when the gridelectrodes were not provided but when the latter were provided, thecontrast wasimproved to 490 volts. Since the discharge opening alsoserves as an optical slit so that the length of the grid electrodes mustbe substantially equal to that of the optical slit.

In a simultaneous-light-image-projection-anddischarge device of the typeshown in FIGS. 4a, 4a and 4b, an a-c voltage is applied to the coronadischarge wires so that the discharge efficiency may be much improved.Again, the spacing between the grid .wires may be equal or varied asshown respectively in FIGS. 40 and 4a, and the device thus shown issimilar in construction to that shown in FIG 3 except that the auxiliaryelectrodes are covered with an insulating member 25. In the device shownin FIG. 4, the auxiliary electrodes 20 and 20' are grounded and a highvoltage is applied to the corona discharge wires 18 from an a-c voltagesource so that the positive voltage of a half cycle of the ac highvoltage produces a positive corona discharge. As a result, thephotosensitive layer 24 and the insulating member 25 are positivelycharged. The negative half cycle produces a negative corona discharge sothat the electric fields produced around the corona discharge wires 18and the insulating layer 25 become higher than when only the auxiliaryelectrodes 20 and 20' are provided because the insulating layer 25 hasbeen charged positively in the preceding positive half cycle. In thiscase, the positively charged insulating layer 25 is neutralized by thenegative corona discharge and then negatively charged. The negativelycharged insulating layer 25 improves the positive corona discharge in amanner similar to that described above. The above positive and negativecorona discharge operations are cycled and the efficiency in coronadischarge can be much improved as compared with the device having noinsulating layer 25. It is preferable to use a high frequency powersource as the a-c power source for thesimultaneous-image-projection-and-discharge device of the type shown inFIG. 4. In the device of the type shown in FIGS. 3a and 3a, theauxiliary electrodes 20 and 20, may be made solely of insulatingmaterial in order to increase the efficiency in a-c corona discharge.Since the effect of the grounded grid electrodes 22 can be attained asdescribed hereinbefore with reference to FIG. 3, the efficiency indischarge may be much improved and the zero potential discharge may beaccomplished in an ideal manner.

As described above, according to the present invention, the operationand efficiency of the discharge may be remarkably improved. Theadvantages of the simultaneous-image-projection-and discharge devices inac cordance with the present invention may be summarized as follows:

I. The discharge operation is reliable and dependable even if theenvironmental conditions and especially temperature conditions arevaried.

2. The contrast of the image may be improved.

3. Irregular discharge due to the contamination and flaws of thedischarge electrodes.

Next referring to FIG. 5, the advantages of the electrophotographiccopying machine of the present invention incorporating thesimultaneous-image-projectionand-discharge device will be described withrelation to the prior art photocopying machine. The data of thevariation in surface potential of the photosensitive layer was obtainedby the electrophotographic copying machine of the present invention andby the prior art photocopying machine of the type in which aphotosensitive layer including an insulating layer is first charged by afirst charger and charged again with the polarity opposite to that ofthe first charging, or by an a-c corona discharger, simultaneously whena light image is projected, whereupon the whole surface of thephotosensitive layer is illuminated. When the prior artsimultaneous-image-projection-and-discharge device is used after thesurface of the photosensitive layer has been uniformly imparted with thehigh voltage charge of the order of 2,400 volts so that the areasrepresenting white areas of the copy of the electrostatic latent imagemay be discharged to zero volt, the areas representing the black areasof the copy are discharged somewhat to the opposite polarity. So far ithas been impossible to discharge both the bright and dark areas to apredetermined level. However, by thesimultaneous-imageprojection-and-discharge device in accordance with thepresent invention provided with the grounded grid electrodes, bothbright and dark areas may be uniformly discharged to zero voltage. Inthe prior art machine, the contrast in voltage of the electrostaticlatent image is low after the charge has been eliminated in theproximity of and from the interface between the photoconductive layerand the insulating layer by the wholesurface exposure, because of thepotential difference in the bright and dark areas after the second step,that is, the simultaneous-image-projection-and-discharge. However, whenthe simultaneous-image-projectionand-discharge device having thegrounded grid electrodes in accordance with the present invention isused, both the surface potentials at the dark and bright areas aredischarged to zero volt so that the electrostatic latent image after thewhole-surface illumination step may have the improved high contrasttone.

F IG. 6 illustrates the effect of environmental humidity upon thesurface potential at the white area after thesimultaneous-image-projection-and-discharge step, and prior to thewhole-surface illumination. In the prior art machine. the effect of thehumidity on the discharge efficiency is remarkable, but according to thepresent invention, the effect of the humidity may be negligible and thedischarge efficiency is stable over the wide range of humidityvariation.

From the foregoing description, it is seen that the electrophotographiccopying machine in accordance with the present invention can reproducecopies at a high speed, with high contrast tone and uniform sensitivity.Since the effect of the humidity variation are minimized, theelectrophotographic copying may be advantageously used in the areas ofhigh temperatures.

The present invention is not limited to the embodiments described above,and various modifications and variations may be effected withoutdeparting the true spirit of the present invention.

We claim:

1. An electrophotographic copying machine comprising a photosensitivemember having an insulating surface;

a first charger means for uniformly imparting a first charge upon thesurface of said photosensitive member;

8 simultaneous-light-image-projection-and-discharge means for projectinga light image of an object to be copied upon the surface of saidphotosensitive member and simultaneously imparting a second charge todischarge said first charge imparted by said first charger means, saidsimultaneous-lightimage-projection-and-discharge means comprising coronadischarge electrodes, auxiliary electrodes surrounding said coronadischarge electrodes and defining an optical aperture and an opening fordischarge, and means for equalizing the surface charges includinggrounded grid electrodes disposed in the proximity of said dischargeopening defined by said auxiliary electrodes; and

means for blanket exposing the whole surface of said photosensitivemember.

2. An electrophotographic copying machine as set forth in claim 1wherein said auxiliary electrodes are made of an electrically conductingmaterial and are grounded.

3. An electrophotographic copying machine as set forth in claim 1wherein said grid electrodes comprise a plurality of wire electrodes.

4. An electrophotographic copying machine as set forth in claim 1wherein the spacing between the adjacent wire grid electrodes are madenarrower in the direction of the movement of said photosensitive memberrelative to said simultaneous-light-image-projection-and-dischargemeans.

5. An electrophotographic copying machine comprising a photosensitivemember having an insulating surface;

a first charger means for imparting a uniform first charge upon thesurface of said photosensitive member;

simultaneous-light-image-projection-and-discharge means for projecting alight image upon the surface of said photosensitive member andsimultaneously effecting an a-c corona discharge onto the surface ofsaid photosensitive member. saidsimultaneouslight-image-projection-and-discharge means comprising coronadischarge electrodes, grounded auxiliary electrodes surrounding saidcorona discharge electrodes and defining an optical aperture and anopening for discharge, an insulating member disposed over each of saidauxiliary electrodes in opposed relation with said corona dischargeelectrodes, and means for equalizing the surface charges, includinggrounded grid electrodes disposed in the proximity of said dischargeopening; and

means for illuminating the whole surface of said photosensitive member.

6. An electrophotographic copying machine as set forth in claim 5wherein said grounded grid electrodes comprise a plurality of wireelectrodes.

7. An electrophotographic copying machine as set forth in claim 6wherein the spacing between the adjacent wire grid electrodes are madenarrower in the direction of the movement of said photosensitive memberrelative to said simultaneous-light-image-projection-and-dischargemeans.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo.3,797,9.27 D te March 19, 1974 lnventm-(s) ToRU TAKAHASH ET AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the Abstract, line 4, after "and" insert -the;

In the Abstract, line ll, after "apparatus" insert so that-;

Column 1, line 26, after "material" insert Column 3, line 35,"abovedescribed"should read abovedescribed--;

Column 4, line 26, "by the" should read with an--+;

Column 4, line 51, after "charger 8" insert Column 4, lines 51/52,delete "or impart the corona charge imparted by the first charger 8,";

Column 4, line 52, after "corona" insert discharge to the photosensitivelayer of the drum 4, simultaneously--;

Column 4, line 59, after "device" delete "l0";

Column 4, line 60, after "device" insert. -l0-;

Column 5, line 28, after "views" insert -and--;

Column 6, line 63, after "electrodes" insert may be eliminated-;

Colunm 8, line 26, "inclaim 1" should read in claim 3.

Signed and sealed this 30th day of July 1971+.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION r nNo.3,797,9.27 Dated March 1974 I e t TORU 'TAKAHASHLET AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the Abstract, line 4, after "and" insert the;

In the Abstract, line 11, after "apparatus" insert so that;

Column 1, line 26, after "material" insert Column 3, line 35,"abovedescribed" should read abovedescribed-;

Column 4, line 26, "by the" should read with an--;

Column 4, line 51, after "charger 8" insert Column 4, lines 51/52,delete "or impart the corona charge imparted by the first charger 8,";

Column 4, line 52, after "corona" insert discharge to the photosensitivelayer of the drum 4, simultaneously-;

Column 4, line 59, after "device" delete "l0";

Column 4, line 60, after "device" insert l0-;

Column 5, line 28, after "views" insert -and--;

Column 6, line 63, after "electrodes" insert may be eliminated--;

Column 8, line 26, "in-claim 1" should read in claim 3--.

Signed and sealed this 30th day of July 1971+.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. An electrophotographic copying machine comprising a photosensitivemember having an insulating surface; a first charger means for uniformlyimparting a first charge upon the surface of said photosensitive member;simultaneous-light-image-projection-and-discharge means for projecting alight image of an object to be copied upon the surface of saidphotosensitive member and simultaneously imparting a second charge todischarge said first charge imparted by said first charger means, saidsimultaneous-lightimage-projection-and-discharge means comprising coronadischarge electrodes, auxiliary electrodes surrounding said coronadischarge electrodes and defining an optical aperture and an opening fordischarge, and means for equalizing the surface charges includinggrounded grid electrodes disposed in the proximity of said dischargeopening defined by said auxiliary electrodes; and means for blanketexposing the whole surface of said photosensitive member.
 2. Anelectrophotographic copying machine as set forth in claim 1 wherein saidauxiliary electrodes are made of an electrically conducting material andare grounded.
 3. An electrophotographic copying machine as set forth inclaim 1 wherein said grid electrodes comprise a plurality of wireelectrodes.
 4. An electrophotographic copying machine as set forth inclaim 1 wherein the spacing between the adjacent wire grid electrodesare made narrower in the direction of the movement of saidphotosensitive member relative to saidsimultaneous-light-image-projection-and-discharge means.
 5. Anelectrophotographic copying machine comprising a photosensitive memberhaving an insulating surface; a first charger means for imparting auniform first charge upon the surface of said photosensitive member;simultaneous-light-image-projection-and-discharge means for projecting alight image upon the surface of said photosensitive member andsimultaneously effecting an a-c corona discharge onto the surface ofsaid photosensitive member, saidsimultaneous-light-image-projection-and-discharge means comprisingcorona discharge electrodes, grounded auxiliary electrodes surroundingsaid corona discharge electrodes and defining an optical aperture and anopening for discharge, an insulating member disposed over each of saidauxiliary electrodes in opposed relation with said corona dischargeelectrodes, and means for equalizing the surface charges includinggrounded grid electrodes disposed in the proximity of said dischargeopening; and means for illuminating the whole surface of saidphotosensitive member.
 6. An electrophotographic copying machine as setforth in claim 5 wherein said grounded grid electrodes comprise aplurality of wire electrodes.
 7. An electrophotographic copying machineas set forth in claim 6 wherein the spacing between the adjacent wiregrid electrodes are made narrower in the direction of the movement ofsaid photosensitive member relative to saidsimultaneous-light-image-projection-and-discharge means.